1. Field of Invention
The present invention relates to a memory device, and more particularly, relates to a ROM (a read only memory) semiconductor.
2. Description of Related Art
In general, the contents of ROM semiconductors are written, when memory devices are manufactured, as dormant patterns which cannot be rewritten by users. FIG. 11 shows an example of an equivalent circuit diagram of a conventional ROM semiconductor using diodes. In this diagram, memory cells are formed at cross-points of X-direction linear electrodes and Y-direction linear electrodes, i.e., a simple matrix structure is formed, and in this structure, a binary state is stored in each memory cell depending on whether an X-direction linear electrode and a Y-direction linear electrode are connected to each other by a diode.
A schematic cross-sectional view of a ROM semiconductor is shown in FIG. 12. An X-direction linear electrode 700 and a Y-direction linear electrode 701 are formed with a semiconductor layer 702 provided therebetween and are arranged so that a binary state is stored in accordance with the presence or the absence of an insulating film 712. For example, a memory cell 710 corresponds to a cell connected by a diode in FIG. 11, and a memory cell 711 corresponds to a cell not connected by a diode.
In a process for manufacturing conventional ROM semiconductors, a photomask is manufactured in accordance with a write pattern (a pattern written in ROM semiconductor), a photoresist layer is selectively exposed in conformity with the write pattern, and an insulating layer is then selectively etched, whereby a dormant pattern is written.